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X-linked infantile spinal muscular atrophy is a condition that affects only boys and is characterized by severe muscle weakness and absent reflexes (areflexia). Affected children often have multiple joint deformities (contractures) from birth that cause joint stiffness (arthrogryposis) and impair movement. In severe cases, affected infants are born with broken bones. The muscle weakness worsens over time; affected children reach some early motor developmental milestones, such as sitting unassisted, but these skills are often lost (developmental regression).

Additional features of X-linked infantile spinal muscular atrophy include an unusually small chin (micrognathia), abnormal curvature of the spine (scoliosis or kyphosis), and undescended testes (cryptorchidism).

Weakness of the chest muscles used for breathing often leads to life-threatening breathing problems. Children with X-linked infantile spinal muscular atrophy usually do not survive past early childhood due to respiratory failure, although, in rare cases, affected individuals can survive into adolescence.

Systemic mastocytosis is a blood disorder that can affect many different body systems. Individuals with the condition can develop signs and symptoms at any age, but it usually appears after adolescence.

Signs and symptoms of systemic mastocytosis often include extreme tiredness (fatigue), skin redness and warmth (flushing), nausea, abdominal pain, bloating, diarrhea, the backflow of stomach acids into the esophagus (), nasal congestion, shortness of breath, low blood pressure (hypotension), lightheadedness, and headache. Some affected individuals have attention or memory problems, anxiety, or depression. Many individuals with systemic mastocytosis develop a skin condition called urticaria pigmentosa, which is characterized by raised patches of brownish skin that sting or itch with contact or changes in temperature. Nearly half of individuals with systemic mastocytosis will experience severe allergic reactions (anaphylaxis).

There are five subtypes of systemic mastocytosis, which are differentiated by their severity and the signs and symptoms. The mildest forms of systemic mastocytosis are the indolent and smoldering types. Individuals with these types tend to have only the general signs and symptoms of systemic mastocytosis described above. Individuals with smoldering mastocytosis may have more organs affected and more severe features than those with indolent mastocytosis. The indolent type is the most common type of systemic mastocytosis.

The severe types include aggressive systemic mastocytosis, systemic mastocytosis with an associated hematologic neoplasm, and mast cell leukemia. These types are associated with a reduced life span, which varies among the types and affected individuals. In addition to the general signs and symptoms of systemic mastocytosis, these types typically involve impaired function of an organ, such as the , . The organ dysfunction can result in an abnormal buildup of fluid in the abdominal cavity (ascites). Aggressive systemic mastocytosis is associated with a loss of bone tissue (osteoporosis and osteopenia) and multiple bone fractures. Systemic mastocytosis with an associated hematologic neoplasm and mast cell leukemia both involve blood cell disorders or blood cell cancer (). Mast cell leukemia is the rarest and most severe type of systemic mastocytosis.

Individuals with the milder forms of the condition generally have a normal or near normal life expectancy, while those with the more severe forms typically survive months or a few years after diagnosis.

The causes of rosacea are complex and not well understood. Both genetic and environmental factors appear to influence the disorder, although many of these factors have not been identified.

Studies suggest that rosacea is associated with abnormalities of blood vessels (the vascular system) and the immune system. In people with this condition, blood vessels expand (dilate) too easily, which can cause redness and flushing of the skin. Rosacea is also associated with abnormal inflammation. Inflammation is a normal immune system response to injury and foreign invaders, such as bacteria. Abnormal inflammation impairs the skin’s ability to act as a protective barrier for the body. Researchers believe that a combination of blood vessel abnormalities, abnormal inflammation, and a disruption of the skin barrier underlie the signs and symptoms of rosacea.

Among the genes thought to play roles in rosacea are several genes in a family called the . The HLA complex helps the immune system distinguish the body’s own proteins from proteins made by foreign invaders. Each HLA gene has many different variations, allowing each person’s immune system to react to a wide range of foreign proteins. Certain variations in HLA genes likely contribute to the abnormal inflammation that is characteristic of rosacea.

Another group of genes that appear to be involved in the development of rosacea are glutathione S-transferases (GSTs). The proteins produced from these genes help protect cells from oxidative stress. Oxidative stress occurs when unstable molecules called reactive oxygen species (ROS) accumulate to levels that can damage or kill cells. Variants in several GST genes have been associated with an increased risk of developing rosacea. Researchers suspect that these variants reduce the ability of GSTs to protect skin cells from oxidative stress, leading to cell damage and inflammation.

Environmental (nongenetic) factors can also increase the risk of developing rosacea and trigger its symptoms. Among the best-studied risk factors for rosacea is exposure to ultraviolet (UV) radiation from the sun. UV radiation causes oxidative stress that can damage skin cells. Studies suggest that having an overgrowth of certain microorganisms that live on facial skin, particularly mites called Demodex folliculorum, may also contribute to the development of rosacea. These mites stimulate an abnormal immune response and disrupt the normal skin barrier. Other factors that can trigger the signs and symptoms of rosacea or make them worse include heat exposure, spicy food, cigarette smoking, and alcohol, all of which cause blood vessels in the skin to dilate.

49,XXXXY syndrome is a chromosomal condition in boys and men that causes intellectual disability, developmental delays, physical differences, and an inability to father biological children (infertility). Its signs and symptoms vary among affected individuals.

Boys and men with 49,XXXXY syndrome have mild or moderate intellectual disability with learning difficulties. Speech and language development is particularly affected. Most affected boys and men can understand what other people say more easily than they themselves can speak. People with 49,XXXXY syndrome tend to be shy and friendly, but problems with speech and communication can contribute to behavioral issues, including irritability, difficulty tolerating frustration, defiant behavior, and outbursts or temper tantrums.

49,XXXXY syndrome is also associated with weak muscle tone (hypotonia) and problems with coordination that delay the development of motor skills, such as sitting, standing, and walking. Affected infants and young boys are often shorter than their peers, but some catch up in height later in childhood or adolescence.

Other physical differences associated with 49,XXXXY syndrome include abnormal fusion of certain bones in the forearm (radioulnar synostosis), an unusually large range of joint movement (), elbow abnormalities, curved pinky fingers (fifth finger ), and flat feet (). Affected individuals have distinctive facial features that can include widely spaced eyes (), outside corners of the eyes that point upward (), skin folds covering the inner corner of the eyes (epicanthal folds), and a flat bridge of the nose. Dental abnormalities are also common in this disorder.

49,XXXXY syndrome disrupts male sexual development. The penis is often short and underdeveloped, and the testes may be undescended, which means they are abnormally located inside the pelvis or abdomen. The testes are small and do not produce enough testosterone, which is the hormone that directs male sexual development. The shortage of testosterone often leads to incomplete puberty. Starting in adolescence, affected boys and men may have sparse body hair, and some experience breast enlargement (gynecomastia). Their testes do not produce sperm, so all men with 49,XXXXY syndrome are infertile.

48,XXXY syndrome is a chromosomal condition in boys and men that causes intellectual disability, developmental delays, physical differences, and an inability to father biological children (infertility). Its signs and symptoms vary among affected individuals.

Most boys and men with 48,XXXY syndrome have mild intellectual disability with learning difficulties. Speech and language development is particularly affected. Most affected boys and men can understand what other people say more easily than they themselves can speak. The problems with speech and communication can contribute to behavioral issues, including irritability and outbursts or temper tantrums. Boys and men with 48,XXXY syndrome tend to have anxiety, a short attention span, and impaired social skills.

48,XXXY syndrome is also associated with weak muscle tone (hypotonia) and problems with coordination that delay the development of motor skills, such as sitting, standing, and walking. Affected boys and men tend to be taller than their peers, with an average adult height of over 6 feet.

Other physical differences associated with 48,XXXY syndrome include abnormal fusion of certain bones in the forearm (radioulnar synostosis), an unusually large range of joint movement (), elbow abnormalities, curved pinky fingers (fifth finger ), and flat feet (). Affected individuals may have distinctive facial features, including widely spaced eyes (), outside corners of the eyes that point upward (), and skin folds covering the inner corner of the eyes (epicanthal folds). However, some boys and men with 48,XXXY syndrome do not have these differences in their facial features.

48,XXXY syndrome disrupts male sexual development. The penis is shorter than usual, and the testes may be undescended, which means they are abnormally located inside the pelvis or abdomen. The testes are small and do not produce enough testosterone, which is the hormone that directs male sexual development. The shortage of testosterone often leads to incomplete puberty. Starting in adolescence, affected boys and men may have sparse body hair, and some experience breast enlargement (gynecomastia). Their testes typically do not produce sperm, so most men with this condition are infertile.

Obsessive-compulsive disorder (OCD) is a mental health condition characterized by features called obsessions and compulsions. Obsessions are intrusive thoughts, mental images, or urges to perform specific actions. While the particular obsessions vary widely, they often include fear of illness or contamination; a desire for symmetry or getting things “just right;” or intrusive thoughts involving religion, sex, or aggression. Compulsions consist of the repetitive performance of certain actions, such as checking or verifying, washing, counting, arranging, acting out specific routines, or seeking assurance. These behaviors are performed to relieve anxiety, rather than to seek pleasure as in other compulsive behaviors like gambling, eating, or sex.

While almost everyone experiences obsessive feelings and compulsive behaviors occasionally or in particular contexts, in OCD they take up more than an hour a day and cause problems with work, school, or social life. People with OCD generally experience anxiety and other distress around their need to accommodate their obsessions or compulsions.

About half the time, OCD becomes evident in childhood or adolescence, and most other cases appear in early adulthood. It is unusual for OCD to start after age 40. It tends to appear earlier in males, but by adulthood it is slightly more common in females. Affected individuals can experience periods when their symptoms increase or decrease in severity, but the condition usually does not go away completely.

Some people with OCD have additional mental health disorders such as generalized anxiety, depression, phobias, panic disorders, or schizophrenia. OCD can also occur in people with other neurological conditions such as Tourette syndrome and similar disorders, traumatic brain injury, stroke, or dementia.

Changes in any of several genes are involved in the formation of Wilms tumor. Wilms tumor is often associated with mutations in the WT1 gene, CTNNB1 gene, or AMER1 gene. These genes provide instructions for making proteins that regulate gene activity and promote the growth and division (proliferation) of cells. WT1, CTNNB1, and AMER1 gene mutations all lead to the unchecked proliferation of cells, allowing tumor development.

Changes on the short (p) arm of chromosome 11 are also associated with developing Wilms tumor. Two genes in this area, IGF2 and H19, are either turned on or off depending on whether the copy of the gene was inherited from the mother or the father. This parent-specific difference in gene activation is a phenomenon called genomic imprinting. In some cases of Wilms tumor, abnormalities in the process of genomic imprinting on chromosome 11 lead to a loss of H19 gene activity and increased activity of the IGF2 gene in kidney cells. The resulting loss of H19 gene activity, which normally restrains cell growth, and increase in IGF2 gene activity, which promotes cell growth, together lead to uncontrolled cell growth and tumor development in people with Wilms tumor.

In most cases of Wilms tumors involving one kidney and nearly all cases involving both kidneys, the tumors are thought to arise from immature kidney tissue that never developed properly. These immature tissues are known as nephrogenic rests. It is likely that genetic changes are involved in the presence of nephrogenic rests and that additional genetic changes trigger nephrogenic rests to develop into a tumor.

Genetic conditions that share a genetic cause with Wilms tumor can also have this cancer as a feature. These conditions include WAGR syndrome, Denys-Drash syndrome, and Frasier syndrome, which are caused by mutations in the WT1 gene. Wilms tumor has also been seen in individuals with Beckwith-Wiedemann syndrome, which can be caused by changes in the genomic imprinting of the IGF2 and H19 genes. Wilms tumor can be a feature of other genetic conditions caused by mutations in other genes.

Many children with Wilms tumor do not have identified mutations in any of the known genes. In these cases, the cause of the condition is unknown. It is likely that other, unknown genes are also associated with the development of Wilms tumor.

The inheritance pattern of subcortical band heterotopia depends on its genetic cause.

When subcortical band heterotopia is caused by mutations in the DCX gene, it is inherited in an X-linked pattern. The DCX gene is located on the X chromosome, which is one of the two sex chromosomes. In females, who have two copies of the X chromosome, one altered copy of the gene in each cell can lead to the condition, sometimes with less severe symptoms than affected males. In males, who have only one X chromosome, a mutation in the only copy of the gene in each cell usually causes a more severe condition called isolated lissencephaly sequence (ILS). Most males with subcortical band heterotopia have a DCX gene mutation that is not inherited and is present in only some of the body’s cells, a situation known as mosaicism. A characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons.

When subcortical band heterotopia is caused by a PAFAH1B1 gene mutation, it is generally not inherited but arises from a mutation in the body’s cells that occurs after conception, which leads to mosaicism. This alteration is called a somatic mutation. PAFAH1B1 gene mutations that occur in all of the body’s cells (germline mutations) usually cause ILS.

Farsightedness, also known as hyperopia, is an eye condition that causes blurry near vision. People who are farsighted have more trouble seeing things that are close up (such as when reading or using a computer) than things that are far away (such as when driving).

For normal vision, light passes through the clear cornea at the front of the and is focused by the lens onto the surface of the , which is the lining of the back of the eye that contains light-sensing cells. Some people who are farsighted have eyeballs that are too short from front to back. Others have a cornea or lens that is abnormally shaped. These changes cause light entering the eye to be focused too far back, behind the retina instead of on its surface. It is this difference that causes nearby objects to appear blurry. In a person with this condition, one eye may be more farsighted than the other.

If it is not treated with corrective lenses or surgery, farsightedness can lead to eye strain, excess tearing, squinting, frequent blinking, headaches, difficulty reading, and problems with hand-eye coordination. However, some children with the eye changes characteristic of farsightedness do not notice any blurring of their vision or related signs and symptoms early in life. Other parts of the visual system are able to compensate, at least temporarily, for the changes that would otherwise cause light to be focused in the wrong place.

Most infants are born with a mild degree of farsightedness, which goes away on its own as the eyes grow. In some children, farsightedness persists or is more severe. Children with a severe degree of farsightedness, described as high hyperopia, are at an increased risk of developing other eye conditions, particularly “lazy eye” (amblyopia) and eyes that do not look in the same direction (strabismus). These conditions can cause significant visual impairment.

In general, older adults also have difficulty seeing things close up; this condition is known as . Presbyopia develops as the lens of the eye becomes thicker and less flexible with age and the muscles surrounding the lens weaken. Although it is sometimes described as “farsightedness,” presbyopia is caused by a different mechanism than hyperopia and is considered a separate condition.